Emergency power system

An emergency power system provides a reliable backup source of electricity when the primary power source fails.

The first types of emergency power systems were used on World War II naval ships consisting of diesel engines that provided backup for the main steam engine generators. The earliest systems relied on manual transfer switches that had to be “turned on,” but eventually automatic transfer switches were developed.

Emergency power systems are based on electrical generators or some type of electrical storage system. For buildings, gas and diesel engines are usually used and gas turbines are often utilized when large structures are involved. Electrical storage devices include deep cycle batteries, flywheel storage and hydrogen fuel cells.

Fuel cells do not emit toxic gases and thus may be located within the building, and they also do not require separate fuel storage areas. Deep cycle batteries are designed to discharge at a consistent voltage as compared to starter batteries that deliver current in surges. Deep cycle batteries can also be recharged at a lower current than normal batteries. They are designed with a solid lead plates whicle normal batteries have more porous plates.

With most electrical generators, when the main power supply fails a solenoid throws the automatic transfer switch starting the backup power generator. Because many generators take some time to start up, there can be some lag time and voltage drop during the switch to the emergency power system. Some devices and systems will fail in such instances and thus other backup systems like surge protectors and inverters are needed. Inverters are high power electronic oscillators that convert electricity from DC sources like batteries into AC electricity.

However, some equipment cannot tolerate even minute and momentary drops in voltage, so in these cases an uninterruptible power supply (UPS) is required. An uninterruptible power supply uses one or more battery backups to provide an instant power feed after the failure of the main power generating system. The UPS is designed to provide such power only for a limited amount of time, normally less than 15 minutes, as the backup generator starts up and reaches its full capacity.

Large uninterruptible power supply systems can provide several megawatts of power capable of supplying large buildings and other large operations. Most UPS systems are redundant, so if one battery backup system fails another is ready to instantly take its place. In some cases, for example, when the equipment uses DC, the battery backup is connected directly to the equipment and “floats” on the regular generator’s DC rectifier output. So that if the main power generator fails, no transfer switch is needed and the battery is able to automatically carry the required load as the backup generator starts up.

Utility stations that provide public electricity are naturally designed for automatic, instantaneous switching of their regular power generators. In some cases however, when there is a simultaneous failure of all the main generators a “black-out” situation occurs. Black-outs are usually caused by bad relays in the grid lines caused by excess grid disturbance. In such cases, an emergency power system must respond rapidly to prevent equipment damage and the development of environmental hazards, for example, the buildup of hydrogen gas.

Some types of devices that use emergency power systems include emergency lighting, exit signs, fire alarm and suppression systems, smoke control systems, elevators and emergency access equipment. Hospitals, data centers, water pumping stations and communications switching stations are examples of operations that would normally depend on an emergency power system.

The emergency power system has allowed some operations to continue running without even momentary power interruption since 1920s.

DCPowerSupplies.org